Field of the Invention
The invention relates to a method for monitoring the conversion capacity of a catalytic converter for an internal combustion engine, in which an inlet temperature of exhaust gas is measured upstream of the catalytic converter; a first outlet temperature of the exhaust gas is measured downstream of the catalytic converter; a second outlet temperature is calculated from the inlet temperature, according to a temperature model; and the first outlet temperature and the second outlet temperature are compared, and the conversion capacity of the catalytic converter is assessed on the basis of the comparison.
Legal requirements demand that the conversion capacity of a catalytic converter of an internal combustion engine be monitored during operation in the motor vehicle itself with suitable self-diagnosis.
It is known from an article entitled "Konzept zur Katalysatoruberwachung durch Reaktionswarmeermittlung" Concept for Catalytic Converter Monitoring by Ascertaining Reaction Heat! by Grigorios C. Koltsakis, et al., in MTZ, 58, 1997, p. 178-184, to use reaction heat generated in the catalytic converter by the catalytic reaction, as a measure for diagnosing the conversion capacity of the catalytic converter. The temperature upstream of the catalytic converter and the temperature downstream of the catalytic converter are measured and the reaction heat in the catalytic converter is calculated from them, which represents a measure of the conversion capacity of the catalytic converter.
A device for monitoring the degree of conversion of an exhaust gas catalytic converter even under unstable operating conditions is known from German Published, Non-Prosecuted Patent Application DE 41 22 787 A1. The exhaust gas temperature is ascertained at a point downstream of the catalytic converter through the use of a temperature sensor and is delivered to an evaluation unit. The evaluation unit also communicates with the output of a computer, which operates as a function of signals of a temperature sensor upstream of the catalytic converter and a sensor for the respective flow rate and as a function of the catalytic converter geometry, to calculate the temperature that would be established at the site of the temperature sensor downstream of the catalytic converter if the catalytic converter were inoperative. The evaluation unit furnishes a signal for the applicable degree of conversion from the difference between the two temperature signals.